A study of the mechanism of osmoregulation on the cellular and organ level. This involves: 1. Transport of ions, water and organic molecules across epithelial membranes and across cell membranes in aquatic osmoconformers, hypo- and hyperosmoregulators. 2. Intracellular versus extracellular concentrations of ions and organic molecules in vertebrates and invertebrates adapted to fresh water and to various salinities. 3. Effect of heavy metals upon ion transport mechanisms in various organs such as gills kidneys, bladders, intestine, and cell membranes. Binding of heavy metals to these organs and the form in which it is bound.